[FIX] mrp_subcontracting: wrong subcontracted productions

Previously, when we find out subcontracted productions of moves, we get
all production_id from the origin moves of the moves. When user use
multple steps manufacturing, moves may also have their move_orig_ids.
In this case, we will consider its production_id as subcontracted
production.
To fix, we filered the moves, consider only move that is_subcontract is
true.

closes odoo/odoo#67066

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>